This invention relates to a data communication system which includes a plurality of independent control units, each control unit including a microcomputer so as to control a plurality of independent functional operations and executes a composite functional operation by uniting the plurality of functional operations systematically through the communication among the control units.
In recent years, image forming apparatuses such as digital copying machines have been constructed, in order to avoid the complication and large-size of the apparatus itself resulting from the multiple and high-level imaging function, as system units in which respective functional blocks are treated as independent blocks and the respective blocks are connected systematically so as to execute a composite functional operation as a whole.
In the system unit of this type, there are provided a controller including a microcomputer provided specially for each block and a reloadable storage device such as a RAM random access memory) for storing an information necessary for the controllers to execute the respective functional operations. Further, the respective blocks are connected so that, for example, a serial data communication can be conducted among them to transmit the necessary information to one another. For example, there is known a digital copying machine in which an operation block for controlling output and input of various information concerning a copying operation and a drive block for controlling the actual copying operation based on the information from the operation block are so connected that the communication can be conducted therebetween (Japanese Unexamined Utility Model Publication No. 4-70654).
As a manner for serial data communication, there has been known as a handshaking manner by which the data communication is conducted while each communication end is conforming the receiving state of the other end. There are generally two types of handshaking manner: one by which the handshaking is performed for each independent data, and the other by which a number of data to be transmitted and received is set in advance depending upon a communication mode and the handshaking is performed each time the predetermined number of data are transmitted.
FIG. 17 is a flow chart showing the former conventional handshaking manner.
The description will be given taking the digital copying machine as an example. When a size data A representing the size of a cassette attached to the copying machine is required (YES in Step S200), the controller for the operation block (hereinafter referred to as an operation controller) transmits a transmission requirement data for size data A to the controller for the drive block (hereinafter referred to as a drive controller) (Step S202). Upon the receipt of the transmission requirement data for the size data A (YES in Step S206), the drive controller immediately generates and transmits the size data A to the operation controller (Step S208).
When the operation controller receives the size data A completely (Step S204), the data communication for the size data A is completed. Each time the operation controller requires a certain data, it transmits a transmission requirement data for this data to the drive controller and receives the data therefrom.
FIG. 18 is a flow chart showing the latter conventional handshaking manner.
In a ROM (read only memory) of each of the operation and drive controllers, there is stored a communication mode P for communicating preprogrammed data units DAT1 (A, B . . . Y) and DAT2 (a, b . . . , y), each including 25 data, alternately. The data units DAT1, DAT2 are constantly transmitted in accordance with the communication mode P.
First of all, the operation controller transmits a code data for the "communication mode P" to the drive controller (Step S210). Upon the receipt of the code data for the "communication mode P" (Step S212), the drive controller sets a state where the communication is enabled in accordance with the communication mode P and transmits a setting completion data of the communication mode P to the operation controller (Step 8214).
Upon the receipt of the setting completion data (Step S216), the operation controller transmits the first data A of the data PAT1 to the drive controller (Step S218). Upon the receipt of the data A (Step S220), the drive controller transmits the first data a of the data PAT2 to the operation controller (Step 8222). Upon the receipt of the data a (Step S224), the operation controller transmits the next data B to the drive controller (Step S226). Upon the receipt of the data B (Step S228), the drive controller transmits the next data b to the operation controller (Step S230).
In this manner, the operation and drive controllers transmit and receive the data DAT1, DAT2 alternately in the specified order. A series of data transmissions is completed when the operation controller receives the last data y from the drive controller (Step S232), and this routine returns to Step S210 in order to conduct the next serial data communication.
Since the communication is conducted while confirming the received state of the other end for each data according to the former conventional handshaking manner, it takes a long time to conduct a data communication for each individual data. When a huge amount of data are transmitted, a processing speed for the data communication is reduced.
More specifically, the more complicated and the higher level the system unit becomes, the more types and the greater amount of data are allowed to be transmitted. Such a data communication requires a long time, thereby reducing considerably the processing efficiency of the respective controllers. For example, in the digital copying machine, 500 to 600 bytes of data are transmitted between the operation and drive blocks. If these data are transmitted in the lump, there is required a communication time of 2.5 to 3 seconds (in 5 ms/byte). During this period, no other control is executable.
Some contents of the data to be transmitted are not always necessary during the data communication. They may be transmitted during a specific period or at specified intervals. For example, between the operation and drive blocks of the digital copying machine are transmitted data necessary for each copying operation such as a copy mode, the number of copies to be made, an exposure level, and a copy start, data necessary to control respective actuators driven to carry out the imaging operation such as a main charger level data, a toner density level data, first/second sheet feeding timing data, and a fixing temperature data, and operation history data such as a total number of developing operations performed, the total number of fed copy sheets, and the number of abnormality. The data necessary for each copying operation need to be transmitted constantly, whereas it is sufficient to transmit the data necessary to control the actuators when the digital copying machine is started unless the control content is not changed, and it is sufficient to transmit the operation history data regularly.
On the other hand, according to the latter conventional handshaking manner, the data are transmitted alternately until the communication of the predetermined number of data is completed. Thus, the communication time is shorter compared to the former manner. However, transmission conditions such as the number of data to be transmitted, contents of data, and the transmission order in the communication mode P are preset and stored in the ROMs of the operation and drive controllers. Accordingly, when the content of the communication mode P needs to be changed, this manner cannot respond to such a request easily.
More specifically, when the content of the communication mode P should be changed, in order to execute an image forming operation more smoothly, such that data units DAT1' (A, B . . . , Y, Z) and DAT2' (a, b . . . , y, z), each containing 26 data, are transmitted alternately, it is necessary to rewrite the contents of the ROMs or to replace the ROMs with new ones. Generally, this cannot be done promptly.